"Bring my goat " Porgy exclaims in the final scene of Gershwin's opera Porgy and Bess. Bess, whom he loves, has left for New York City, and he's determined to find her. When his request is met with astonishment--New York is a great distance from South Carolina's Catfish Row--Porgy remains undaunted. He mounts his goat-cart and leads the community in an ecstatic finale, "Oh Lawd, I'm on my way."

Stephen Sondheim has called "Bring my goat " "one of the most moving moments in musical theater history." For years it was assumed that DuBose Heyward--the author of the seminal novella and subsequent play, Porgy, and later the librettist for the opera Porgy and Bess--penned this historic line. In fact, both it and "Oh Lawd, I'm on my way" were added to the play eight years earlier by that production's unheralded architect: Rouben Mamoulian. Porgy and Bess as we know it would not exist without the contributions of this master director.

Culling new information from the recently opened Mamoulian Archives at the Library of Congress, award-winning author Joseph Horowitz shows that, more than anyone else, Mamoulian took Heyward's vignette of a regional African-American subculture and transformed it into an epic theater work, a universal parable of suffering and redemption. Part biography, part revelatory history, "On My Way" re-creates Mamoulian's visionary style on stage and screen, his collaboration with George Gershwin, and the genesis of the opera that changed the face of American musical life.